CA1226106A - Pressure molding process using salt cores and a composition for making cores - Google Patents
Pressure molding process using salt cores and a composition for making coresInfo
- Publication number
- CA1226106A CA1226106A CA000450682A CA450682A CA1226106A CA 1226106 A CA1226106 A CA 1226106A CA 000450682 A CA000450682 A CA 000450682A CA 450682 A CA450682 A CA 450682A CA 1226106 A CA1226106 A CA 1226106A
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- Canada
- Prior art keywords
- core
- process according
- salt
- bath
- mixture
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C33/00—Moulds or cores; Details thereof or accessories therefor
- B29C33/44—Moulds or cores; Details thereof or accessories therefor with means for, or specially constructed to facilitate, the removal of articles, e.g. of undercut articles
- B29C33/52—Moulds or cores; Details thereof or accessories therefor with means for, or specially constructed to facilitate, the removal of articles, e.g. of undercut articles soluble or fusible
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Molds, Cores, And Manufacturing Methods Thereof (AREA)
- Compositions Of Macromolecular Compounds (AREA)
Abstract
PRESSURE MOLDING PROCESS USING
SALT CORES AND A COMPOSITION
FOR MAKING CORES
Abstract A process for pressure molding an article around a hardened salt mold core made from a mixture of relatively low melting temperature salt and sand wherein the core is removed from the finished article by immersion of the article containing the core into a molten bath mixture of the core material thereby to melt the core out of the article, recover the core material, and thus replenish the bath for use in making additional cores. The bath is originally constituted by melting a suitable quantity of a dry premix of the salt and sand.
SALT CORES AND A COMPOSITION
FOR MAKING CORES
Abstract A process for pressure molding an article around a hardened salt mold core made from a mixture of relatively low melting temperature salt and sand wherein the core is removed from the finished article by immersion of the article containing the core into a molten bath mixture of the core material thereby to melt the core out of the article, recover the core material, and thus replenish the bath for use in making additional cores. The bath is originally constituted by melting a suitable quantity of a dry premix of the salt and sand.
Description
3LZ;26~
PRESSURE MOLDING PROCESS USING
SALT CORPS AND A COMPOSITION
FOR MAKING CORES
. . _ . .
Field of the Invention This invention relates to pressure molding process and particularly to a molding process utilizing a salt core or molding core made from a mixture of particles of inert material and relatively low melting temperature salt wherein the core is removed from the finished article by melting the core from the article with the core intact therein into a molten bath of the core material.
Prior Art and Background of the Invention United States Patent No. 3,692,551, issued 15 September 18, 1972 to W. R. Weaver, discloses a pressure molding process utilizing a non-detrudable molding core -- which is made by casting a molten salt and sand mixture.
As disclosed in the patent, the use of salt mixtures having a relatively low melting point produces a core having extremely smooth procelain-like surface characteristics which are highly desirable in pressure molding processes.
In addition, the use of sand as part of the core compost-lion results in the core having high compressive strength, a requirement for die casting and for molding articles out of plastics.
According to the patent, the cores are made by dip-coating or surfa~-coating solid sand cores in a molt ten salt bath or, alternatively, by mixing sand into a molten salt bath and casting the resulting liquid mixture into core form.
he patent discloses top removal of the core from the finish article by dissolving, flushing, and Jo ,... .
~L2Z~06 leaching out the core as a solute in water or in weak acid solution or by mechallical vibratioll.
SUMMARY OF THE INVENTION
S In one aspect, our invention resides in the process for making molded articles by forming a moldable material around solidified salt cores comprising the steps of a) preparing a homogeneous molten salt mixture of one or more water soluble salts having low melting temperatures, typically sodium nitrate, potassium nitrate, and optionally sodium nitrate; b) forming a mold core of qivell shape from a portion of the molten salt mixture, and cooling and solidifying the formed core; c) coating the solidified mold core with a wet film of hydrophobic lubricating material, and drying the film on the core; and d) pressure molding a moldable material such as plastic resin around the resulting solid and coated core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containincl the core. The process preferably includes the further step of reclaimincJ the core material, treating as necessary, and returnitlc1 it to the mixture.
The homogeneous molten salt mixture in most cases will comprise about forty percent to sixty-nine ,, j 6~(~6 - pa percent by weight sand. respite the presence of such granular or crystal in material, it has been found that the molten salt cores nevertheless exhibit a smooth porcelain-like finish which results in an extremely smooth and friction less surface on the interior of the molded plastic article. This may be of considerable importance where the article is used as a conduit for fluid such as cooling water.
According to another aspect of the invention, a dry, packaged premix composition for producing mold cores for use in the aforementioned process comprises an unfused blended dry mixture of inert material and granulated mold core salt, said salt being of the water soluble, low melting temperature type.
- _ 3 _ 6 Preferably a-t least one of the inert materials is ox such physical character as to add -tensile strength and legibility to -the cores. The preferred inert materials are essentially two-dimensional in character;
i.e., in -the form of flakes, needles, or strands. Suitable materials are mica flakes, glass fibers, carbon fibers, plastic fibers, metal needles, and calcium silicate. Such materials are preferably present in the bath in quantities comprising about forty percent to about sixty percent by weight.
According to another aspect of the invention, it has been found preferable for reasons of economy and otherwise to recover as much of the core material from the molded plastic articles as is possible, and returning such material to active use. In some cases, this is accomplished by washing the core materials out of the molded plastic articles, filtering the resulting soul-tion/mixture to remove and preferably recover -the inert particles, and thereafter boiling the water of of -the mixture to recover the salt. The salt can then be reused as desired.
In other arrangements, particularly those using thermal setting resins for -the molded plastic articles, the molded articles, complete with cores, may be placed 25 in or over the bath and heated so as to cause the core materials to melt and drain from the articles into either an intermediate container for treatment purposes or dir-easily back into the core forming bath. To our surprise, it has been found possible to actually immerse articles made of thermoplastic resin in-to the molten core material bath thereby to make direct recovery of the core materials.
In other cases, it is desirable to heat the article out-side of the bath such as by microwave or radiant energy heating to melt out the core.
According to a final aspect of our invention, a premix of salt and inert materials in the proper qua-.~, ~26~0~i PRICK -pa-lilies is prepared and bagged for shipment to molding sites where the premixed materials may be transferred into a furnace or bath directly and in sufficient qua-lilies to make up the bath of appropriate size.
Brief Description of the Drawing The single figure is a flow chart in block diagram form illustrating a preferred embodiment of the pressure molding process of the present invention.
Detailed Description Referring to the drawing, the present process for making core-free (hollow) molded articles by form-in a moldable material around solidified salt cores or mold cores made of particles of inert material intimately - mixed and covered with used salt comprising the steps of:
A. preparing a bath by means of mixing and heating (step 10) the particles and salt (step 12~ to obtain a homogeneous molten bath mixture;
B. forming a mold core step 14) of given shape from a portion of the molten bath mixture and cooling and solidifying the formed core;
C. pressure molding a moldable material (step 16~ around the resulting solid core to cause the PRICK ~~~
moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core;
and D. thereafter heating the molded article (step 18) positioned in or over the molten bath under temperature conditions sufficient to melt and recover the core from the article into the bath (by gravity flow with agitation if necessary) but insufficient to adversely affect the article thus freed of the core; and optionally washing (step 20) the article to remove residual salt and/or sand.
For purposes of the invention, as indicated, one uses sand as a core material. In a preferred embodiment, one uses washed foundry sand that, with respect to particle size, is sufficiently fine for molding, preferably in the range of mesh sizes from 40 to 500, and more preferably from 80 to 1~0. Also one uses a low melting salt mixture, which may comprise alkali metal nitrates, nitrites, chlorides, carbonates, sulfates and phosphates. Preferably, one uses a mixture comprising alkali metal nitrates and/or nitrites such as sodium and potassium nitrates and nitrites, optionally with one or more alkali metal chlorides. Eutectic salt mixtures are preferred. Commercially available grades are suitable, especially granulated salt mixtures forum-fated to melt at a specified temperature in a range of graded temperatures. In a preferred embodiment, the core material comprises one or more alkali~ing salts or agents for strengthening purposes, not more than about 5% by weight, such as an alkali metal or alkaline earth metal hydroxide or carbonate, preferably sodium or calcium hydroxide. It is thought that the alcoholizing agent serves to provide an advantageously strengthening chemical bond between the inert material and the fusible salt. The core material may be an hydrous or may contain water in small amounts as, for example, ranging from 1 or 2% up to about 10% or more by weight. For purposes of the invention, the term "low melting" refers to salt mixtures selected such that, when constituted as intact OWE, mold cores in articles ready for melt-out to the molten bath, they can be melted out ox the articles to recover the core material without adversely affecting the no suiting core-free molded articles. Preferred sand/salt bath mixtures are those melting in the range from about 250 degrees to about 600 degrees F. or more. The inert material and salt mixture may vary in its composition, preferably containing about 40 to about I by weight inert material. The mixture, as is hereinafter desk cried in greater detail, is placed in a suitable heating vessel such as a commercial heat treating fur-nice and brought to a molten state for casting purposes.
The mixture is maintained in a relatively homogeneous condition by means of a mechanical agitator which may be selected from any of various types which are commercially available.
From the melt, material is taken as needed and used to form cores of the desired size and con fig-unction. In accordance with the teaching of the Weaver Patent 3,692,551, such cores are preferably made by casting the molten salt/sand mix using a hinged mold.
Thereafter, the cores are used to pressure mold a mold-able material, such as a metal, or a thermoplastic or thermosetting filled or unwilled plastic, in a compress soon molding or injection molding machine (or a discus-soon of suitable plastics and compression molding apt pyrites, see Plastics, Thea Ed., Van Nostrand, New York, 1981; Modern Plastics Encyclopedia, 1982-1983, McGraw-Hill, 1982). In some instances, to facilitate the molding, it is desirable to use a barrier coating or slip aid to coat the salt core prior to molding. For this purpose, the salt core is covered with a lubrica-tying coating which will make for easier injection mold-in and a smoother surface and will prevent attack on the salt core. Any ox various coating materials are PRICK -Spa-suitable such as silicones, paraffin waxes, or heavy oils dissolved (e.g. 3-5% by weight) in mineral spirits which after applying in a wet film and air drying leave a smooth hard dry hydrophobic surface. The I
Prickly -6-coating serves not only to provide a smoother better interior surface for the molded part but also to result in lower core breakage. The cores may be used in a variety of forms of metal casting and plastic molding involving a wide range of temperature and pressure con-Dennis. For plastic molding especially, one uses a core that has a melt-out temperature sufficiently lower than the critical temperature, i.e. the softening point or degradation point, of the particular plastic being molded so that under the melt-out conditions employed the molded plastic article is not adversely affected.
The choice of core will vary from case to case but in general, for a typical melt-out cycle time, e.g. 2 5 minutes, will be such what the melt-out temperature is lower by at least about 50 degrees F. than the critical temperature of the plastic article undergoing core no-moral. During the pressure molding step, the core is suitably supported within the mold so that the mold material under compression essentially surrounds and captures the core and thereafter becomes structurally rigid. In accordance with one embodiment of the invent lion, the thus finished article with the core intact therein is immersed into, i.e., positioned within, the core source bath at step 18 for a time sufficient to effectively melt the core material out of the article and thus directly make up or recover said material back into the bath without the need for leaching or mechanical vibration or other recovery procedure. In another embodiment, the finished molded article with the core intact therein is positioned, no, within the bath, but over the bath such that when the core is melted (by means presently to be descried), the melted core ma-tonal is allowed Lo flow and drop by gravity into the bath, thus recovering the core material for further ongoing operation. In this embodiment, heating of the article for melt-out of the core is done by radiant energy, preferably microwave heating in the zone above the bath. As indicated, during the molding step 16 and prior to the melt-out step 18, the molded article be-' -~ZZ6~6 comes structurally rigid (that is, sets up or is hardened or cured or partially cured). The molten bath (step 18), as indicated, or the mentioned microwave zone or its equivalent melt-out zone, is kept below the temperature which would unduly soften or melt or other-wise adversely affect the molded article. The article is thereafter washed or rinsed, if necessary, at step 20 to remove all traces of salt or sand therefrom A small amount of sand/salt mix may be lost in the course of the lo process, although this amount is far less than would be lost or wasted if the cores were leached out or broken out and discarded. For example/ there may be losses both in casting the core and by drag out between the immersion melt-out step 18 and rinse or wash step 20.
In a preferred embodiment at step 10, to insure uniformity of core composition and to eliminate the need for weighing and mixing separate quantities of sand and salt, we mix dry sand and granulated salt and bulk-package the mixture, preferably in small (e.g., 501b.~
bugs for shipment and storage. Thus, at the work site, one or more bags or partial bags of the premix ad van-tageously may be added directly to the bath (step 12) for make up purposes or used to originally constitute the bath at start-up.
The invention and best mode of practicing the same are illustrated by the following examples.
Example 1. A dry premix is made by blending washed foundry sand (by weight 55 parts, 80-100 mesh, Wed Ron C-3~ sand) and granulated salt (27 parts sodium nitrate, 18 parts potassium nitrate). The resulting dry blended premix, packaged in shipper bags (50 lb.
capacity), is suitable for shipment and long term storage, without appreciable particle desegregation.
The premix melting at about 430 degrees F. can be used fox making a molten salt bath operating at a useful working temperature of about 470-480 degrees I. or higher. To a bath apparatus (jacketed resistance band heated steel pot, 15 inches deep by 15 inches in diameter) are added 100 pounds of the sand/salt premix.
glues 6 The bath is heated to melt the premix and the molten bath mixture is maintained at a temperature of about ~80 degrees F. and stirred with a heavy duty air motor agitator that keeps the sand uniformly suspended. For core molding, a split mold of rectilinear shape is used.
The mold, of heavy aluminum, is of a design that can be quickly opened and closed by means of spring loaded quick release hinges. The mold is jacketed with circulating pressurized hot (230 degrees F.) water. For lo core molding, the molten bath mixture is gravity fed to the mold by pouring from a preheated ladle into an opening (spruce hole) in the top of the mold. The thus filled mold is allowed to cool for 20-25 seconds and is then opened and the molded core part removed and held for transfer to compression molding apparatus.
Typically, the molded core parts are uniform and very smooth. The compressive strengths at room temperature and 330 degrees F. are greater than 2~,000 and 6,000 psi, respectively. The cores can be remelted in 2 to 5 minutes at 475-480 degrees F. A molded core part, prepared as described and maintained at 330 degrees F.
is transferred from the core mold to the mold cavity of an injection molding machine. Thermoses finlike resin bead material (Resin RX6~0, Rogers, Co., Manchester, Corn.) at a temperature of 330 degrees F. and a pressure of 15,000 psi is then injection molded into the mold cavity and around the molded salt core. After I
seconds, the resulting finlike resin molded article cools in the mold sufficiently to polymerize and solidity and become structurally rigid. The molded plastic article with the salt core intact is then removed and immersed for 2 to 5 minutes in the salt bath mixture maintained at 480 degrees F. While immersed, the article is purposely held in a position allowing for good drainage of liquid from cavities of the article, especially for good drainage just as the article is being removed from the bath. During the melt-out period, the salt core melts completely so that as the plastic article is being removed from the salt bath I
mixture, any remaining melted salt core material quickly drains from the article into the bath for replenishment of the bath. Any traces of salt or sand remaining on the molded article are washed off with water.
Example 2. A dry premix is made by blending 50% by weight of washed foundry sand (80-100 mesh, Wed Ron C-30 sand), 48~ of granulated salt (sodium nitrate/sodium nitrite/potassium nitrate, 30:20:50), and
PRESSURE MOLDING PROCESS USING
SALT CORPS AND A COMPOSITION
FOR MAKING CORES
. . _ . .
Field of the Invention This invention relates to pressure molding process and particularly to a molding process utilizing a salt core or molding core made from a mixture of particles of inert material and relatively low melting temperature salt wherein the core is removed from the finished article by melting the core from the article with the core intact therein into a molten bath of the core material.
Prior Art and Background of the Invention United States Patent No. 3,692,551, issued 15 September 18, 1972 to W. R. Weaver, discloses a pressure molding process utilizing a non-detrudable molding core -- which is made by casting a molten salt and sand mixture.
As disclosed in the patent, the use of salt mixtures having a relatively low melting point produces a core having extremely smooth procelain-like surface characteristics which are highly desirable in pressure molding processes.
In addition, the use of sand as part of the core compost-lion results in the core having high compressive strength, a requirement for die casting and for molding articles out of plastics.
According to the patent, the cores are made by dip-coating or surfa~-coating solid sand cores in a molt ten salt bath or, alternatively, by mixing sand into a molten salt bath and casting the resulting liquid mixture into core form.
he patent discloses top removal of the core from the finish article by dissolving, flushing, and Jo ,... .
~L2Z~06 leaching out the core as a solute in water or in weak acid solution or by mechallical vibratioll.
SUMMARY OF THE INVENTION
S In one aspect, our invention resides in the process for making molded articles by forming a moldable material around solidified salt cores comprising the steps of a) preparing a homogeneous molten salt mixture of one or more water soluble salts having low melting temperatures, typically sodium nitrate, potassium nitrate, and optionally sodium nitrate; b) forming a mold core of qivell shape from a portion of the molten salt mixture, and cooling and solidifying the formed core; c) coating the solidified mold core with a wet film of hydrophobic lubricating material, and drying the film on the core; and d) pressure molding a moldable material such as plastic resin around the resulting solid and coated core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containincl the core. The process preferably includes the further step of reclaimincJ the core material, treating as necessary, and returnitlc1 it to the mixture.
The homogeneous molten salt mixture in most cases will comprise about forty percent to sixty-nine ,, j 6~(~6 - pa percent by weight sand. respite the presence of such granular or crystal in material, it has been found that the molten salt cores nevertheless exhibit a smooth porcelain-like finish which results in an extremely smooth and friction less surface on the interior of the molded plastic article. This may be of considerable importance where the article is used as a conduit for fluid such as cooling water.
According to another aspect of the invention, a dry, packaged premix composition for producing mold cores for use in the aforementioned process comprises an unfused blended dry mixture of inert material and granulated mold core salt, said salt being of the water soluble, low melting temperature type.
- _ 3 _ 6 Preferably a-t least one of the inert materials is ox such physical character as to add -tensile strength and legibility to -the cores. The preferred inert materials are essentially two-dimensional in character;
i.e., in -the form of flakes, needles, or strands. Suitable materials are mica flakes, glass fibers, carbon fibers, plastic fibers, metal needles, and calcium silicate. Such materials are preferably present in the bath in quantities comprising about forty percent to about sixty percent by weight.
According to another aspect of the invention, it has been found preferable for reasons of economy and otherwise to recover as much of the core material from the molded plastic articles as is possible, and returning such material to active use. In some cases, this is accomplished by washing the core materials out of the molded plastic articles, filtering the resulting soul-tion/mixture to remove and preferably recover -the inert particles, and thereafter boiling the water of of -the mixture to recover the salt. The salt can then be reused as desired.
In other arrangements, particularly those using thermal setting resins for -the molded plastic articles, the molded articles, complete with cores, may be placed 25 in or over the bath and heated so as to cause the core materials to melt and drain from the articles into either an intermediate container for treatment purposes or dir-easily back into the core forming bath. To our surprise, it has been found possible to actually immerse articles made of thermoplastic resin in-to the molten core material bath thereby to make direct recovery of the core materials.
In other cases, it is desirable to heat the article out-side of the bath such as by microwave or radiant energy heating to melt out the core.
According to a final aspect of our invention, a premix of salt and inert materials in the proper qua-.~, ~26~0~i PRICK -pa-lilies is prepared and bagged for shipment to molding sites where the premixed materials may be transferred into a furnace or bath directly and in sufficient qua-lilies to make up the bath of appropriate size.
Brief Description of the Drawing The single figure is a flow chart in block diagram form illustrating a preferred embodiment of the pressure molding process of the present invention.
Detailed Description Referring to the drawing, the present process for making core-free (hollow) molded articles by form-in a moldable material around solidified salt cores or mold cores made of particles of inert material intimately - mixed and covered with used salt comprising the steps of:
A. preparing a bath by means of mixing and heating (step 10) the particles and salt (step 12~ to obtain a homogeneous molten bath mixture;
B. forming a mold core step 14) of given shape from a portion of the molten bath mixture and cooling and solidifying the formed core;
C. pressure molding a moldable material (step 16~ around the resulting solid core to cause the PRICK ~~~
moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core;
and D. thereafter heating the molded article (step 18) positioned in or over the molten bath under temperature conditions sufficient to melt and recover the core from the article into the bath (by gravity flow with agitation if necessary) but insufficient to adversely affect the article thus freed of the core; and optionally washing (step 20) the article to remove residual salt and/or sand.
For purposes of the invention, as indicated, one uses sand as a core material. In a preferred embodiment, one uses washed foundry sand that, with respect to particle size, is sufficiently fine for molding, preferably in the range of mesh sizes from 40 to 500, and more preferably from 80 to 1~0. Also one uses a low melting salt mixture, which may comprise alkali metal nitrates, nitrites, chlorides, carbonates, sulfates and phosphates. Preferably, one uses a mixture comprising alkali metal nitrates and/or nitrites such as sodium and potassium nitrates and nitrites, optionally with one or more alkali metal chlorides. Eutectic salt mixtures are preferred. Commercially available grades are suitable, especially granulated salt mixtures forum-fated to melt at a specified temperature in a range of graded temperatures. In a preferred embodiment, the core material comprises one or more alkali~ing salts or agents for strengthening purposes, not more than about 5% by weight, such as an alkali metal or alkaline earth metal hydroxide or carbonate, preferably sodium or calcium hydroxide. It is thought that the alcoholizing agent serves to provide an advantageously strengthening chemical bond between the inert material and the fusible salt. The core material may be an hydrous or may contain water in small amounts as, for example, ranging from 1 or 2% up to about 10% or more by weight. For purposes of the invention, the term "low melting" refers to salt mixtures selected such that, when constituted as intact OWE, mold cores in articles ready for melt-out to the molten bath, they can be melted out ox the articles to recover the core material without adversely affecting the no suiting core-free molded articles. Preferred sand/salt bath mixtures are those melting in the range from about 250 degrees to about 600 degrees F. or more. The inert material and salt mixture may vary in its composition, preferably containing about 40 to about I by weight inert material. The mixture, as is hereinafter desk cried in greater detail, is placed in a suitable heating vessel such as a commercial heat treating fur-nice and brought to a molten state for casting purposes.
The mixture is maintained in a relatively homogeneous condition by means of a mechanical agitator which may be selected from any of various types which are commercially available.
From the melt, material is taken as needed and used to form cores of the desired size and con fig-unction. In accordance with the teaching of the Weaver Patent 3,692,551, such cores are preferably made by casting the molten salt/sand mix using a hinged mold.
Thereafter, the cores are used to pressure mold a mold-able material, such as a metal, or a thermoplastic or thermosetting filled or unwilled plastic, in a compress soon molding or injection molding machine (or a discus-soon of suitable plastics and compression molding apt pyrites, see Plastics, Thea Ed., Van Nostrand, New York, 1981; Modern Plastics Encyclopedia, 1982-1983, McGraw-Hill, 1982). In some instances, to facilitate the molding, it is desirable to use a barrier coating or slip aid to coat the salt core prior to molding. For this purpose, the salt core is covered with a lubrica-tying coating which will make for easier injection mold-in and a smoother surface and will prevent attack on the salt core. Any ox various coating materials are PRICK -Spa-suitable such as silicones, paraffin waxes, or heavy oils dissolved (e.g. 3-5% by weight) in mineral spirits which after applying in a wet film and air drying leave a smooth hard dry hydrophobic surface. The I
Prickly -6-coating serves not only to provide a smoother better interior surface for the molded part but also to result in lower core breakage. The cores may be used in a variety of forms of metal casting and plastic molding involving a wide range of temperature and pressure con-Dennis. For plastic molding especially, one uses a core that has a melt-out temperature sufficiently lower than the critical temperature, i.e. the softening point or degradation point, of the particular plastic being molded so that under the melt-out conditions employed the molded plastic article is not adversely affected.
The choice of core will vary from case to case but in general, for a typical melt-out cycle time, e.g. 2 5 minutes, will be such what the melt-out temperature is lower by at least about 50 degrees F. than the critical temperature of the plastic article undergoing core no-moral. During the pressure molding step, the core is suitably supported within the mold so that the mold material under compression essentially surrounds and captures the core and thereafter becomes structurally rigid. In accordance with one embodiment of the invent lion, the thus finished article with the core intact therein is immersed into, i.e., positioned within, the core source bath at step 18 for a time sufficient to effectively melt the core material out of the article and thus directly make up or recover said material back into the bath without the need for leaching or mechanical vibration or other recovery procedure. In another embodiment, the finished molded article with the core intact therein is positioned, no, within the bath, but over the bath such that when the core is melted (by means presently to be descried), the melted core ma-tonal is allowed Lo flow and drop by gravity into the bath, thus recovering the core material for further ongoing operation. In this embodiment, heating of the article for melt-out of the core is done by radiant energy, preferably microwave heating in the zone above the bath. As indicated, during the molding step 16 and prior to the melt-out step 18, the molded article be-' -~ZZ6~6 comes structurally rigid (that is, sets up or is hardened or cured or partially cured). The molten bath (step 18), as indicated, or the mentioned microwave zone or its equivalent melt-out zone, is kept below the temperature which would unduly soften or melt or other-wise adversely affect the molded article. The article is thereafter washed or rinsed, if necessary, at step 20 to remove all traces of salt or sand therefrom A small amount of sand/salt mix may be lost in the course of the lo process, although this amount is far less than would be lost or wasted if the cores were leached out or broken out and discarded. For example/ there may be losses both in casting the core and by drag out between the immersion melt-out step 18 and rinse or wash step 20.
In a preferred embodiment at step 10, to insure uniformity of core composition and to eliminate the need for weighing and mixing separate quantities of sand and salt, we mix dry sand and granulated salt and bulk-package the mixture, preferably in small (e.g., 501b.~
bugs for shipment and storage. Thus, at the work site, one or more bags or partial bags of the premix ad van-tageously may be added directly to the bath (step 12) for make up purposes or used to originally constitute the bath at start-up.
The invention and best mode of practicing the same are illustrated by the following examples.
Example 1. A dry premix is made by blending washed foundry sand (by weight 55 parts, 80-100 mesh, Wed Ron C-3~ sand) and granulated salt (27 parts sodium nitrate, 18 parts potassium nitrate). The resulting dry blended premix, packaged in shipper bags (50 lb.
capacity), is suitable for shipment and long term storage, without appreciable particle desegregation.
The premix melting at about 430 degrees F. can be used fox making a molten salt bath operating at a useful working temperature of about 470-480 degrees I. or higher. To a bath apparatus (jacketed resistance band heated steel pot, 15 inches deep by 15 inches in diameter) are added 100 pounds of the sand/salt premix.
glues 6 The bath is heated to melt the premix and the molten bath mixture is maintained at a temperature of about ~80 degrees F. and stirred with a heavy duty air motor agitator that keeps the sand uniformly suspended. For core molding, a split mold of rectilinear shape is used.
The mold, of heavy aluminum, is of a design that can be quickly opened and closed by means of spring loaded quick release hinges. The mold is jacketed with circulating pressurized hot (230 degrees F.) water. For lo core molding, the molten bath mixture is gravity fed to the mold by pouring from a preheated ladle into an opening (spruce hole) in the top of the mold. The thus filled mold is allowed to cool for 20-25 seconds and is then opened and the molded core part removed and held for transfer to compression molding apparatus.
Typically, the molded core parts are uniform and very smooth. The compressive strengths at room temperature and 330 degrees F. are greater than 2~,000 and 6,000 psi, respectively. The cores can be remelted in 2 to 5 minutes at 475-480 degrees F. A molded core part, prepared as described and maintained at 330 degrees F.
is transferred from the core mold to the mold cavity of an injection molding machine. Thermoses finlike resin bead material (Resin RX6~0, Rogers, Co., Manchester, Corn.) at a temperature of 330 degrees F. and a pressure of 15,000 psi is then injection molded into the mold cavity and around the molded salt core. After I
seconds, the resulting finlike resin molded article cools in the mold sufficiently to polymerize and solidity and become structurally rigid. The molded plastic article with the salt core intact is then removed and immersed for 2 to 5 minutes in the salt bath mixture maintained at 480 degrees F. While immersed, the article is purposely held in a position allowing for good drainage of liquid from cavities of the article, especially for good drainage just as the article is being removed from the bath. During the melt-out period, the salt core melts completely so that as the plastic article is being removed from the salt bath I
mixture, any remaining melted salt core material quickly drains from the article into the bath for replenishment of the bath. Any traces of salt or sand remaining on the molded article are washed off with water.
Example 2. A dry premix is made by blending 50% by weight of washed foundry sand (80-100 mesh, Wed Ron C-30 sand), 48~ of granulated salt (sodium nitrate/sodium nitrite/potassium nitrate, 30:20:50), and
2% of chopped glass fiber. The resulting dry blended lo premix, packaged in shipper bags t50 lb. capacity), is suitable for shipment and long term storage, without appreciable particle desegregation. The premix melting at about 305 degrees F. can be used for making a molten salt bath operating at a useful working temperature of about 350-380 degrees I or higher. To a bath apparatus (jacketed resistance band heated steel pot, 15 inches deep by 15 inches in diameter) are added 100 pounds of the sand/salt premix. The bath is heated to melt the premix and the molten bath mixture is maintained at a temperature of about 350 degrees F. and stirred to keep the sand uniformly suspended. For core molding, a mold such as the mold described above is wised. The molten bath mixture is gravity fed to the mold by pouring from a preheated ladle into an opening (spruce hold) in the top of the mold. The thus filled mold is allowed to cool for 20-25 seconds and is then opened and the molded core part removed and held for transfer to compression molding apparatus. Typically, the molded core parts are uniform and very smooth. The compressive strengths at room temperature and 250 degrees F. are greater than 20,000 and ~,000 psi, respectively. The cores can be remelted in 20-30 seconds at 350-380 degrees F. A
molded core part, prepared as described and maintained at 250 degrees F. is transferred from the core mold to the mold cavity of an injection molding machine. A
commercially available polyester resin bulk molding compound (BMC) at a temperature of 2~0 degrees F. and a pressure of 15,000 psi is then injection molded into the mold cavity and around the molded salt core. After ~2Z6~
setting, the molded article polymerizes in the mold surf-ficiently to solidify and become structurally rigid.
The article with the salt core intact is then removed and immersed for 2 to 5 minutes in the salt bath mixture maintained at 350 degrees F. to melt the core. While immersed, the article is positioned to allow the core liquid to drain from cavities of the article, and the article is washed and dried.
Further examples which follow the foregoing procedure according to the invention, at different temperatures with appropriate moldable materials, are as follows:
I
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molded core part, prepared as described and maintained at 250 degrees F. is transferred from the core mold to the mold cavity of an injection molding machine. A
commercially available polyester resin bulk molding compound (BMC) at a temperature of 2~0 degrees F. and a pressure of 15,000 psi is then injection molded into the mold cavity and around the molded salt core. After ~2Z6~
setting, the molded article polymerizes in the mold surf-ficiently to solidify and become structurally rigid.
The article with the salt core intact is then removed and immersed for 2 to 5 minutes in the salt bath mixture maintained at 350 degrees F. to melt the core. While immersed, the article is positioned to allow the core liquid to drain from cavities of the article, and the article is washed and dried.
Further examples which follow the foregoing procedure according to the invention, at different temperatures with appropriate moldable materials, are as follows:
I
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or Us at h o Q
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us o in a) us R Jo US Us I us Q I u I
I h V V us-- -- E
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Claims (48)
1. A process for making molded articles by forming a moldable material around solidified salt cores comprising the steps of:
A. preparing a homogeneous molten mixture of one or more water soluble salts having low melting temperatures;
B. forming a mold core of given shape from a portion of the molten salt mixture and cooling and solidifying the formed core;
C. coating the solidified mold core with a wet film of hydrophobic lubricating material and drying the film; and D. pressure molding a moldable material around the resulting solid and coated core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core.
A. preparing a homogeneous molten mixture of one or more water soluble salts having low melting temperatures;
B. forming a mold core of given shape from a portion of the molten salt mixture and cooling and solidifying the formed core;
C. coating the solidified mold core with a wet film of hydrophobic lubricating material and drying the film; and D. pressure molding a moldable material around the resulting solid and coated core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core.
2. A process according to Claim 1 where the moldable material is a thermosetting resin.
3. A process according to Claim 1 where the moldable material is a phenolic thermosetting resin.
4. A process according to Claim 1 where the salt contains sodium nitrate, potassium nitrate and optionally sodium nitrite.
5. A process according to Claim 1 where the molten salt mixture comprises about 40% to 60% by weight sand.
6. A process according to Claim 1 where the molten mixture contains glass fibers.
7. A process according to Claim 1 where the molten mixture contains carbon fibers.
8. A process according to Claim 1 where the molten mixture contains mica flakes.
9. A process according to Claim 1 including the further step of reclaiming the core material and returning it to the mixture.
10. A process according to Claim 1 where the reclaiming step is carried out by immersing the article containing the core in the molten mixture.
11. A process for making molded articles by forming a moldable material around solidified cores made of particles of inert material, at last one of which is of such physical character as to add tensile strength and flexibility to said cores, said inert materials being intimately mixed and covered with fused water soluble, low-melting temperature salt comprising the steps of:
A. preparing a bath by means of mixing and beating the particles and salt to obtain a homogeneous molten bath mixture;
B. forming mold core of given shape from a portion of the molten bath mixture and cooling and solidifying the formed core; and C. pressure molding a moldable material around the resulting solid core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core.
A. preparing a bath by means of mixing and beating the particles and salt to obtain a homogeneous molten bath mixture;
B. forming mold core of given shape from a portion of the molten bath mixture and cooling and solidifying the formed core; and C. pressure molding a moldable material around the resulting solid core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core.
12. A process according to Claim 11 comprising the additional step of:
D. thereafter heating the molded article positioned in or over the molten bath under temperature conditions sufficient to melt and recover the core from the article into the bath but insufficient to adversely affect the article thus freed of the core.
D. thereafter heating the molded article positioned in or over the molten bath under temperature conditions sufficient to melt and recover the core from the article into the bath but insufficient to adversely affect the article thus freed of the core.
13. A process according to Claim 11 where the molded material is a thermosetting resin.
14. A process according to Claim 11 where the molded material is a phenolic thermosetting resin.
15. A process according to Claim 11 where the heating step is carried out by means comprising radiant energy and with the molded article positioned over the bath such that, when the core is melted, the resulting melted core material is allowed to flow by gravity into the bath thus recovering the core material for further ongoing operation.
16. A process according to Claim 15 where the heating step comprises microwave heating in the zone above the bath.
17. A process according to Claim 11 where the bath mixture comprises about 40% to about 60% by weight of inert material.
18. A process according to Claim 11 where the strength and flexibility-adding inert material comprises glass fibers.
19. A process according to Claim 11 where the strength and flexibility-adding inert material comprises carbon fibers.
20. A process according to Claim 11 where the strength and flexibility-adding inert material comprises mica flakes.
21. process according to Claim 11 comprising the steps prior to pressure molding of coating the solidified mold core with a wet film of hydrophobic lubricating material and drying the film.
22. A dry, packaged premix composition for producing mold cores for use in a compression molding process according to Claim 1 comprising an unfused blended dry mixture of inert material and granulated mold core salt, said salt being of the water soluble low-melting temperature type.
23. A premix composition according to Claim 22 where the inert material comprises sand.
24. A premix composition according to Claim 23 where the inert material comprises glass fibers.
25. A premix composition according to Claim 23 where the inert material comprises carbon fibers.
26. A premix composition according to Claim 23 where the inert material comprises mica flakes.
27. A process according to Claim 1 where the core contains a small amount of water.
28. A process for making molded articles by forming a moldable material around solidified salt cores or mold cores made of particles.of inert material intimately mixed and covered with fused salt comprising the steps of:
A. preparing a bath by means of mixing and heating the particles and at least one low-melting temperature, water-soluble salt to obtain a homogeneous molten bath mixture;
B. forming a mold core of given shape from a portion of the molten bath mixture and cooling and solidifying the formed core;
C. pressure molding a moldable material around the resulting solid core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core; and D. thereafter heating the molded article positioned in or over the molten bath under temperature conditions sufficient to melt and recover the core from the article into the bath but insufficient to adversely affect the article thus freed of the core.
A. preparing a bath by means of mixing and heating the particles and at least one low-melting temperature, water-soluble salt to obtain a homogeneous molten bath mixture;
B. forming a mold core of given shape from a portion of the molten bath mixture and cooling and solidifying the formed core;
C. pressure molding a moldable material around the resulting solid core to cause the moldable material to solidify and thus obtain a solid structurally rigid molded article containing the core; and D. thereafter heating the molded article positioned in or over the molten bath under temperature conditions sufficient to melt and recover the core from the article into the bath but insufficient to adversely affect the article thus freed of the core.
29. A process according to Claim 28 comprising the step of removing the core-free article from the bath and optionally washing the article to remove residual salt and/or sand.
30. A process according to Claim 28 where the moldable material is a plastics material.
31. A process according to Claim 28 where the moldable material is a thermosetting resin.
32. A process according to Claim 31 where the moldable material is a phenolic thermosetting resin.
33. A process according to Claim 28 where the salt contains sodium nitrate, potassium nitrate and optionally sodium nitrite.
34. A process according to Claim 28 where the salt contains an alkalizing agent.
35. A process according to Claim 28 where the alkalizing agent comprises sodium hydroxide.
36. A dry, packaged premix composition for producing mold cores for use in a compression molding process according to Claim 28 comprising an unfused blended dry mixture of molding sand and granulated mold core salt of the water soluble, low-melting temperature type, bring about 40%
to about 60% by weight sand.
to about 60% by weight sand.
37. A composition according to Claim 36 wherein the mixture contains about 55% by weight molding sand.
38. A composition according to Claim 37 wherein the mixture contains sodium nitrate and potassium nitrate.
39. A composition according to Claim 37 wherein the mixture contains about 27 parts by weight sodium nitrate and about 18 parts by weight potassium nitrate.
40. A process according to Claim 28 where the heating step is carried out by means comprising radially energy and with the molded article positioned over the bath such that, when the core is melted, the resulting melted core material is allowed to flow and drop by gravity into the bath thus recovering the core material for further ongoing operation.
41. A process according to Claim 40 where the heating step comprises microwave heating in the zone above the bath.
42. A process according to Claim 28 where the bath mixture comprises about 40 to about 60 percent by weight of inert material.
43. A process according to Claim 28 where the inert material comprises sand.
44. A process according to Claim 43 where the inert material comprises glass fibers.
45. A process according to Claim 43 where the inert material comprises carbon fibers.
46. A process according to Claim 43 where the inert material comprises mica flakes.
47. A process according to Claim 28 where the mixture contains an alkalizing agent in the amount of not more than about 5% by weight with respect to the core material.
48. A process according to Claim 28 comprising the steps prior to pressure molding of coating the solidified mold core with a wet film of hydrophobic lubricating material and drying the film.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US47758083A | 1983-03-28 | 1983-03-28 | |
| US477,580 | 1983-03-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1226106A true CA1226106A (en) | 1987-09-01 |
Family
ID=23896515
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000450682A Expired CA1226106A (en) | 1983-03-28 | 1984-03-28 | Pressure molding process using salt cores and a composition for making cores |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0138985A4 (en) |
| JP (1) | JPS60500906A (en) |
| CA (1) | CA1226106A (en) |
| WO (1) | WO1984003857A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2613659A1 (en) * | 1987-04-13 | 1988-10-14 | Peugeot | Method of manufacturing rigid and hollow components which may or may not have drafts (undercuts) |
| GB2246736A (en) * | 1990-07-26 | 1992-02-12 | Dunlop Ltd | Removing a meltable core from a moulded plastics article by immersion in a heated salt solution |
| GB9016636D0 (en) * | 1990-07-28 | 1990-09-12 | Westland Aerostructures Ltd | Method for making perforated composite laminates and moulds for use therein |
| FI922716A (en) * | 1992-06-11 | 1993-12-12 | Harri Sahari | FRAMEWORK FOR PLASTIC PROTECTION |
| US6245265B1 (en) * | 1999-06-23 | 2001-06-12 | International Business Machines Corporation | Method of forming a die-castable hollow core actuator arm with improved damping |
| DE602004031244D1 (en) * | 2003-09-17 | 2011-03-10 | Jun Yaokawa | CORE FOR USE IN CASTING |
| JP5737016B2 (en) * | 2011-07-06 | 2015-06-17 | スズキ株式会社 | Disintegrating core and method for producing the same |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1523519A (en) * | 1924-02-12 | 1925-01-20 | Hartford Rubber Works Co | Core or filler of fusible material for hollow vulcanizable articles |
| FR1100359A (en) * | 1954-03-01 | 1955-09-20 | Process for manufacturing hollow plastic articles and in particular reinforced plastic | |
| GB828685A (en) * | 1955-10-04 | 1960-02-24 | Cole E K Ltd | Improvements relating to the moulding of thermoplastic articles |
| US3136831A (en) * | 1961-07-14 | 1964-06-09 | United Aircraft Corp | Casting method |
| DE1197195B (en) * | 1962-08-31 | 1965-07-22 | Union Carbide Corp | Method for melting out models from precision casting molds |
| US3518338A (en) * | 1964-06-08 | 1970-06-30 | William C Tambussi | Molding process |
| US3356129A (en) * | 1964-06-30 | 1967-12-05 | Schmidt Gmbh Karl | Process of casting metals by use of water-soluble salt cores |
| US3692551A (en) * | 1970-02-24 | 1972-09-19 | Libbey Owens Ford Co | Core for use in pressure molding |
| US4389367A (en) * | 1981-09-30 | 1983-06-21 | Grumman Aerospace Corporation | Fluid molding system |
-
1984
- 1984-03-27 WO PCT/US1984/000452 patent/WO1984003857A1/en not_active Application Discontinuation
- 1984-03-27 JP JP50160084A patent/JPS60500906A/en active Pending
- 1984-03-27 EP EP19840901655 patent/EP0138985A4/en not_active Withdrawn
- 1984-03-28 CA CA000450682A patent/CA1226106A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0138985A4 (en) | 1987-11-23 |
| WO1984003857A1 (en) | 1984-10-11 |
| JPS60500906A (en) | 1985-06-20 |
| EP0138985A1 (en) | 1985-05-02 |
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